Compliant Underactuated Grasper

ABSTRACT

A compliant underactuated grasper includes a palm base and two fingers. Each of the fingers comprises: a proximal phalanx; a distal phalanx; a compliant flexure joint connecting the distal phalanx to the proximal phalanx; and a pin joint connecting the proximal phalanx to the palm base, the pin joint constraining angular movement of the proximal phalanx relative to the palm base to rotation about a pin pivot axis. The grasper further includes at least one actuator to move the fingers. The grasper has fewer actuators than degrees of freedom.

RELATED APPLICATION(S)

The present application claims the benefit of and priority from U.S.Provisional Patent Application No. 61/724,506, filed Nov. 9, 2012, thedisclosure of which is incorporated herein by reference in its entirety.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made with support under Defense Advanced ResearchProjects Agency (DARPA) Contract No. W91CRB-10-C-0141 awarded by DARPAfor the DARPA Autonomous Robot Manipulation-Hardware Track (ARM-H). TheGovernment has certain rights in the invention.

BACKGROUND OF THE INVENTION

End effectors or graspers are commonly mounted on a robotic arm and usedto manipulate and/or grasp objects in a selected environment. Theenvironment may be structured or unstructured.

SUMMARY OF THE INVENTION

According to embodiments of the present invention, a compliantunderactuated grasper includes a palm base and two fingers. Each of thefingers comprises: a proximal phalanx; a distal phalanx; a compliantflexure joint connecting the distal phalanx to the proximal phalanx; anda pin joint connecting the proximal phalanx to the palm base, the pinjoint constraining angular movement of the proximal phalanx relative tothe palm base to rotation about a pin pivot axis. The grasper furtherincludes at least one actuator to move the fingers. The grasper hasfewer actuators than degrees of freedom.

The grasper may further include a pin joint angle sensor associated witheach finger.

The grasper may further include a rotation joint connecting each fingerto the palm base, wherein the finger can be rotated relative to the palmbase about the rotation joint to reorient its pin pivot axis withrespect to the palm base.

In some embodiments, the grasper further includes a thumb and at leastone actuator to move the thumb independently of the fingers. The thumbincludes: a proximal phalanx; a distal phalanx; a compliant flexurejoint connecting the distal phalanx to the proximal phalanx; and a pinjoint connecting the proximal phalanx to the palm base, the pin jointconstraining angular movement of the proximal phalanx relative to thepalm base to rotation about a pin pivot axis.

According to embodiments of the present invention, a compliantunderactuated grasper includes a palm base and two fingers. Each of thefingers includes: a proximal phalanx; a distal phalanx; a compliantflexure joint connecting the distal phalanx to the proximal phalanx; apin joint connecting the proximal phalanx to the palm base, the pinjoint having a dominant degree of freedom about a pin pivot axis; and atendon cable for moving the proximal and distal phalanges such thatmovement of the tendon cable generates angular motion of the proximalphalanx about the pin pivot axis at a greater rate than angular motionof the distal phalanx about the flexure joint. The grasper furtherincludes at least one actuator to move the fingers. The grasper hasfewer actuators than degrees of freedom.

In some embodiments, the flexure joint includes a flexure link formed ofa compliant elastomeric material.

According to some embodiments, the pivot joint connects the proximalphalanx to the palm base for rotation about the pivot joint in a firstdirection and a second direction, the grasper includes a return biasingspring to drive the proximal phalanx in the second direction to a returnposition, the return biasing spring has a first spring rate, the flexurejoint is configured to bias the distal phalanx into an open positionrelative to the proximal phalanx and has a second spring rate, and thesecond spring rate is greater than the first spring rate. In someembodiments, the second spring rate is at least eight times the firstspring rate. In some embodiments, the first spring rate is sufficient toretain the proximal phalanx in the return position in any orientation ofthe grasper with the tendon cable slack, and the second spring rate issufficient to retain the distal phalanx in the open position in anyorientation of the grasper with the tendon cable slack.

According to embodiments of the present invention, a compliantunderactuated grasper includes a palm base and two fingers. Each of thefingers includes: a proximal phalanx; a distal phalanx; a compliantflexure joint connecting the distal phalanx to the proximal phalanx; apivot joint connecting the proximal phalanx to the palm base forrotation about the pivot joint in a first direction and a seconddirection; a tendon cable for moving the proximal phalanx in the firstdirection; a return biasing spring to drive the proximal phalanx in thesecond direction to a return position, wherein the spring rate of thereturn biasing spring is sufficient to retain the proximal phalanx inthe return position in any orientation of the grasper with the tendoncable slack. The grasper further includes at least one actuatorassociated with each tendon cable. The grasper has fewer actuators thandegrees of freedom.

In some embodiments, the return biasing spring includes a torsionspring.

Further features, advantages and details of the present invention willbe appreciated by those of ordinary skill in the art from a reading ofthe figures and the detailed description of the embodiments that follow,such description being merely illustrative of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary, perspective view of a robot including a grasperaccording to embodiments of the invention.

FIG. 2 is a front perspective view of the grasper of FIG. 1.

FIG. 3 is a rear perspective view of the grasper of FIG. 1.

FIG. 4 is a cross-sectional view of the grasper of FIG. 1 taken alongthe line 4-4 of FIG. 1.

FIG. 5 is a cross-sectional view of the grasper of FIG. 1 taken alongthe line 5-5 of FIG. 1.

FIG. 6 is a top plan view of the grasper of FIG. 1.

FIG. 7 is a side elevational view of the grasper of FIG. 1.

FIG. 8 is a rear elevational view of the grasper of FIG. 1.

FIG. 9 is a top perspective view of a finger forming a part of thegrasper of FIG. 1.

FIG. 10 is a bottom perspective view of the finger of FIG. 9.

FIG. 11 is a cross-sectional view of the finger of FIG. 9 taken alongthe line 11-11 of FIG. 9.

FIG. 12 is an enlarged, fragmentary, side view of the finger of FIG. 9.

FIG. 13 is a top plan view of the finger of FIG. 9.

FIG. 14 is a side view of the finger of FIG. 9.

FIG. 15 is a top perspective view of the finger of FIG. 9 and anassociated magnetic breakaway system.

FIG. 16 is an exploded, fragmentary, bottom perspective view of thefinger and magnetic breakaway system of FIG. 15.

FIG. 17 is an exploded, fragmentary, top perspective view of the fingerand magnetic breakaway system of FIG. 15.

FIG. 18 is a cross-sectional view of the magnetic breakaway system ofFIG. 15 taken along the line 18-18 of FIG. 15.

FIG. 19 is a cross-sectional view of the magnetic breakaway system ofFIG. 15 taken along the line 19-19 of FIG. 15.

FIG. 20 is an exploded, fragmentary, cross-sectional, bottom perspectiveview of the magnetic breakaway system of FIG. 15.

FIG. 21 is a top perspective view of a base forming a part of thegrasper of FIG. 1 including submounts forming a part of the magneticbreakaway system.

FIG. 22 is a fragmentary, perspective view of the finger and magneticbreakaway system of FIG. 15 illustrating operation of the magneticbreakaway system.

FIGS. 23-29 illustrate various finger configurations that can beexecuted by the grasper of FIG. 1.

FIGS. 30A and 30B illustrate a sequence of movements of the grasper ofFIG. 1 to grab and pick up an object.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which illustrativeembodiments of the invention are shown. In the drawings, the relativesizes of regions or features may be exaggerated for clarity. Thisinvention may, however, be embodied in many different forms and shouldnot be construed as limited to the embodiments set forth herein; rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the invention to thoseskilled in the art.

It will be understood that when an element is referred to as being“coupled” or “connected” to another element, it can be directly coupledor connected to the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlycoupled” or “directly connected” to another element, there are nointervening elements present. Like numbers refer to like elementsthroughout.

In addition, spatially relative terms, such as “under”, “below”,“lower”, “over”, “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. It will beunderstood that the spatially relative terms are intended to encompassdifferent orientations of the device in use or operation in addition tothe orientation depicted in the figures. For example, if the device inthe figures is turned over, elements described as “under” or “beneath”other elements or features would then be oriented “over” the otherelements or features. Thus, the exemplary term “under” can encompassboth an orientation of over and under. The device may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. As used herein the expression“and/or” includes any and all combinations of one or more of theassociated listed items.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Embodiments of the present invention are directed to end effectors orgraspers. A grasper as disclosed herein may form part of a robot or aprosthetic apparatus. In particular, the grasper may be mounted on arobotic arm and used to manipulate and grasp objects in a structured orunstructured environment. The grasper may be employed as a grasper or“hand” of a humanoid robot and/or may comply with the criteria specifiedunder the DARPA Autonomous Robot Manipulation Hardware (ARM-H) program.

With reference to the figures, a robot 10 (FIG. 1) according toembodiments of the invention is shown therein and includes an arm 12 anda grasper 20 rotatably coupled to the arm 12 by a wrist joint 14.

The grasper 20 includes a base assembly 30, a first finger 70, a secondfinger 80, and a thumb 90. The fingers 70, 80 and the thumb 90 may beidentically constructed except for their placement on the base 30 andmethods and mechanisms of actuation as discussed below. Except asotherwise noted, “finger” and “fingers” also refer to the thumb 90. Thegrasper 20 has a primary or longitudinal axis LG-LG (FIG. 4).

The base 30 includes a first finger actuator 60, a second fingeractuator 62, a thumb agonist actuator 64, a thumb antagonist actuator66, and a finger rotation actuator 68. The actuators 60, 62, 64, 66, 68may be electric motors (e.g., DC motors). Tendon cables 60A and 62A(FIG. 4) are connected to the fingers 70 and 80, respectively, to causecontrolled movement of the fingers 70 and 80 using the actuators 60 and62. Tendon cables 64A, 66A (FIG. 5) are connected to the thumb 90 tocause controlled movement of the thumb 90 using the actuators 64 and 66,respectively. Each of the fingers 70, 80, 90 can be pivoted at arespective proximal pin pivot joint JP about an axis FP-FP (FIG. 2) bythe tendons 60A, 62A, 64A, 66A and the actuators 60, 62, 64, 66.Additionally, the fingers 70 and 80 can be rotated at respectiverotation joints JR about rotation axes FR-FR (FIG. 8) in opposeddirections K by the actuator 68. The fingers 70 and 80 are coupled by alinkage so that they rotate about the joints JR in tandem in oppositedirections from each other. Each finger 70, 80, 90 can also be bentabout a distal compliant flexure joint JC (FIG. 1) as described below.

The base assembly 30 includes a frame 32 and a palm 34 on an operationalside of the frame 32. Three magnet base submounts 160 are mounted in theframe 32 and three associated finger base submounts 40 are mountedthereon (FIG. 15). During normal operation, each submount 160 and itsassociated submount 40 are coupled to function effectively as a singleunit. The submounts 160 of the fingers 70 and 80 are rotatable at thejoints JR.

The fingers 70, 80, 90 may be identically or similarly constructed asdiscussed above. An exemplary finger 70 will be described, and it willbe appreciated that this description will likewise apply to the otherfingers 80 and 90.

With reference to FIGS. 9-14, the finger 70 includes a proximal phalanx110 and a distal phalanx 120 coupled by a compliant flexure link 130 ata compliant distal inter-phalanges flexure joint JC. The finger 70 alsohas a hinge feature 112 coupling the finger 70 to its finger base mount40. The finger 70 has a longitudinal axis LF-LF. More particularly, theproximal phalanx 110 has a proximal end 110A and a distal end 110B. Thedistal phalanx 120 has a proximal end 120A and a distal end 120B. Thehinge feature 112 is provided on the end 110A. The flexure link 130 issecured to the ends 110B and 120A. The end 120B is free. A distalextension or plate member 140 is mounted on the end 120B.

The hinge feature 112 is pivotally coupled to a cooperating hingefeature 42 (FIG. 1) on the finger base submount 40 by a pivot pin 50,which defines the pin pivot axis FP-FP, to form the proximal pin pivotjoint JP. Rotational movement of the finger 70 about the pivot joint JPis constrained to pivoting about the pivot axis FP-FP in a fingerclosing pivot direction F and a finger opening pivot direction H. Thefinger 70 defines a finger lateral plane E parallel to each of thelongitudinal axis LF-LF and the pivot axis FP-FP. It will be appreciatedthat the orientation of the pivot axis FP-FP will vary depending on therotational position of the submount 40 about the axis FR-FR.

In one embodiment, an angle position sensor 54 disposed in the joint JPdetects the angular position of the phalanx 110 with respect to the base30. For example, a magnetic encoder may be mounted on one part of thejoint JP (e.g., the hinge feature 43) and a cooperating magnet may bemounted on another part of the joint JP (e.g., the hinge feature 112).

A biasing member 52 (FIGS. 4 and 7) is provided in the joint JP.According to some embodiments, the biasing member 52 is a torsion springand, in particular, may be a helical torsion spring. The torsion spring52 serves as a counter spring or bias return spring. In the absence ofrestraint from a tendon cable or external force, the torsion spring 52will force the finger 70 to pivot in a direction I to a wide-openposition.

The flexure link 130 is semi-rigid, flexible, resilient and compliant.In some embodiments, the flexure link 130 is formed of an elastomericmaterial. The flexure link 130 flexes or bends preferentially about adistal or flexure joint pivot axis FB-FB in each of an inward, primarydirection M and an outward direction N. The flexure link 130 can alsoflex or bend in opposed sideward or lateral, secondary directions Pperpendicular to or transverse to the finger closing direction F. Thus,the flexure link 130 and the joint JC have a first compliance in a firstdirection M and a second compliance in a second direction P. The seconddirection P is perpendicular or transverse to the tendon cableretraction direction H. The first compliance is greater than the secondcompliance (i.e., less force is required to deflect the flexure link 130in the first direction). When relaxed and nonloaded, the flexure link130 will elastically return to a relaxed position or state as shown inFIGS. 9-11. According to some embodiments, the proximal phalanx 110 andthe distal phalanx 120 are substantially parallel or co-axial when theflexure link 130 is in its return position.

The tendon cable 60A is routed from the actuator 60, through tendonraceways 158, 168 in the submounts 40, 160, along the inner side of thehinge feature 112, through a tendon raceway 118 in the proximal phalanx110, across the flexure joint JC, and through a raceway 128 in thedistal phalanx 120, and is anchored to the distal phalanx 120 (e.g., inthe raceway 128). The actuator 60 can draw the tendon cable 60A throughthe raceways 118, 158, 168 in a direction H to pivot the finger 70 inthe closing direction F. The actuator 60 can then release or pay out thetendon cable 60A in the opposite direction to permit the finger 70 topivot in the opening direction I under the torque of the torsion spring52.

Operation of the finger 70 (and corresponding operation of the finger 80and the thumb 90) will now be discussed in further detail. With thefinger 70 in the fully open position (FIG. 23), the actuator 60 drawsthe tendon cable 60A. The spring force or resistance from the torsionspring 52 is less than the stiffness or spring force or bend resistanceof the flexure link 130. Therefore, assuming the proximal phalanx 110does not encounter external resistance, as the tendon cable 60A appliestension load to the finger 70, the finger 70 will be displaced primarilyabout the pin pivot JP and secondarily about the flexure joint JC. Thatis, the proximal phalanx 110 will pivotally rotate a greater angulardistance about the pivot pin axis FP-FP than the distal phalanx 120pivotally rotates or bends about the flexure joint axis FB-FB.

If and when the proximal phalanx 110 is impeded by an external object(e.g., an object grasped) or strikes a limit (e.g., bottoms out on thebase 30), a greater portion or all of the tension load of the tendoncable 60A will be applied to the flexure joint JC, and the distalphalanx 120 will then bend or rotate about the flexure joint axis FB-FBat a greater rate than the rate at which the proximal phalanx 110rotates about the pin pivot axis FP-FP.

The differential rate of displacement of the phalanges 110 and 120 abouttheir respective pivot axes will depend on the relative effective springforces of the torsion spring 52 and the flexure link 130. According tosome embodiments, the spring force of the flexure joint JC is at least 8times the spring force of the pin pivot joint JP and, in someembodiments, is in the range of from about 8 to 12 times the springforce of the pin pivot joint JP. In some embodiments the spring rate ofthe torsion spring 52 is great enough to fully counteract the force ofgravity on the finger 70 in any intended orientation when the grasper 20is static and not acted on by an external object. According to someembodiments, the spring force of the torsion spring 52 is between about100 and 150 percent of the minimum force necessary to fully counteractthe force of gravity on the finger 70 in any intended orientation whenthe grasper 20 is static and not acted on by an external object. Byminimizing the torsion spring force, the designer can reduce therequired spring rate of the flexure joint JC. In turn, the return forcesthat the actuator 60 must overcome are reduced.

Notably, the spring force of the flexure joint JC can be as high asdesired and/or needed. In particular, the spring force of the flexurejoint JC may be increased as the grasper is scaled up in size and usedto lift larger and heavier objects.

FIGS. 1 and 23-29 show various configurations of the fingers 70, 80, 90that can be assumed or executed by the grasper 20.

FIG. 23 shows a wide open or ready position, wherein the tendon cables60A, 62A, 64A are slack, permitting the torsion springs 52 to force eachfinger 70, 80, 90 to its limit in its open direction.

FIG. 1 shows the fingers 70, 80 in a pinch configuration, which can beachieved when the actuators 60, 62 pull the fingers 70, 80 (via thetendon cables 60A, 62A) closed without significant resistance. For thismaneuver, the finger rotation actuator 68 may first be used to rotatethe fingers 70, 80 into opposition with one another with their pivotaxes FP-FP substantially parallel. FIG. 24 illustrates a modified pinchconfiguration being used to hold and/or manipulate an object 2 such as aflat key.

FIGS. 23, 25 and 26 show the fingers 70, 80, 90 progressing from thewide open configuration (FIG. 23) to a power grasp configuration (FIG.26) wherein the thumb 90 crosses the fingers 70, 80. For this maneuver,the rotation actuator 68 may be used to rotate the fingers 70, 80 intoopposition with the thumb 90 with the pivot axes FP-FP of the fingers70, 80, 90 substantially parallel as shown in FIG. 25. FIG. 27illustrates a modified power grasp configuration being used to holdand/or manipulate an object 4 such as a power tool. The exemplary powertool 4 has a handle 4A and a trigger 4B. The grasper 20 securely holdsthe handle 4A using the fingers 70, 80, 90, and can also be used tooperate the trigger 4B by applying and releasing tension to/from thefinger 80 via the tendon cable 62A so that its distal phalanx 120 willindependently bend at the flexure joint JC and press and release thetrigger 4B (the proximal phalanx 110 being limited or constrained by thehandle 4A).

FIG. 28 shows the fingers 70, 80, 90 in a spherical grasp position. Forthis maneuver, the fingers 70, 80 are rotated so that their pivot axesFP-FP extend at an oblique angle to the pivot axis FP-FP of the thumb90. FIG. 29 illustrates a modified spherical grasp position wherein thegrasper 20 is holding an object 6 such as a ball.

It will be appreciated that the foregoing are not exhaustive of theconfigurations and manipulations that can be achieved using the grasper20.

The relationships between the lengths of the phalanges 110 and 120 andthe finger and thumb base positions can provide advantageousperformance. In some embodiments, these relationships are scalable.

According to some embodiments, the length L1 (FIG. 13) of the proximalphalanx 110 of each finger 70, 80 is greater than the length L2 of thedistal phalanx 120 of the same finger. According to some embodiments,the length L1 is in the range of from about 0.60 to 0.66 times thelength L2.

In some embodiments, the average distance D1 (FIG. 6) from each finger70, 80 base pivot joint JP to the thumb 90 pivot joint JP is in therange of from about 1.30 to 1.44 times the average proximal phalanxlength L1.

According to some embodiments, the major dimension L3 (FIG. 6) of thepalm 34 is in the range of from about 1.21 to 1.33 times the averageproximal phalanx length L1.

In some embodiments, the spacing D2 (FIG. 6) between the pivot joints JPof the fingers 70, 80 is in the range of from about 0.97 to 1.08 timesthe average proximal phalanx length L1.

The provision of fingers each having a proximal pin pivot joint and adistal flexure joint as described may provide certain advantages. Therigid pivot at the base of the finger provides pinch stability andtorsional strength to facilitate fine manipulation and heavy lifting.The flexure joint at the distal joint provides robustness for abuse andenhances the ability of the finger to adapt or conform to unknown shapedobjects. According to some embodiments and as shown, the pin pivot axisFP-FP of each finger is substantially parallel to the primary flexureaxis FB-FB of the finger.

With reference to FIGS. 9-12, according to some embodiments, the grasper20 is provided with a fingernail system 141. The fingernail system 141includes a distal plate member 140 mounted on the distal phalanx 120 ofeach finger 70, 80, 90 adjacent the distal end face 124A thereof. Onlyone of the fingers 70 will be described hereinbelow. However, it will beappreciated that this description applies likewise to the fingers 80 and90.

The distal plate member 140 includes a base portion 144 and a freeterminal lifting edge 142A. The base portion 144 has a slot 144A and isadjustably secured to the back face 124C of the phalanx 120 by afastener 144B such as a screw. The free edge 142A is located adjacentthe end face 124A. In some cases, and as shown, the distal plate member140 has an extension portion 142 terminating in the free edge 142A andoverhanging (cantilevered) or extending axially beyond the location 147where the plate member 140 diverges from the phalanx 120 to form aledge. However, in other embodiments, the free edge 142A can becoincident with or inboard of the location 147.

In some embodiments, the fastener 144B and groove 144A can serve as anadjustment mechanism. More particularly, the fastener 144B can beloosened, the plate member 140 slid to position the edge 142A as desiredrelative to the end face 124A, and the fastener 144B then re-tightenedto secure the plate member 140 in place. It will be appreciated thatother suitable adjustment mechanisms can be employed.

The plate member 142 is relatively thin, at least in the region of thefree edge 142A. According to some embodiments, the free edge 142A has athickness T1 (FIG. 12) in the range of from about 0.02 inch to 0.03inch. In some embodiments, the length L4 of the extension portion 142from the location 147 to the free edge 142A is at least 1 mm and, insome embodiments, from about 1.5 mm to 2.5 mm. According to someembodiments, the free edge 142A is substantially parallel to the flexurejoint axis FB-FB.

According to some embodiments and as shown, the end face 124A and theplate member 140 are relatively configured and arranged to define alaterally extending slot, groove or undercut 146 between the undersideof the extension section 142 and the opposing surface of the end face124A. In some embodiments and as shown, the end face 124A is shaped tocut back axially to form the undercut 146. In some embodiments, the endface 124A is rounded or curvilinear and, in some embodiments, arcuate incross-section (i.e., in a plane perpendicular to the plane E andparallel to the longitudinal axis of the distal phalanx 120).

According to some embodiments, the depth D3 of the undercut 146 is inthe range of from about 1 mm to 3 mm. According to some embodiments, thewidth W1 of the undercut 146 is in the range of from about 10 mm to 25mm.

In some embodiments, the plate member 140 is rigid (e.g., formed ofsteel or stainless steel) and the end face 124A is relatively soft orcompliant (e.g., formed of a pliable rubber). As shown, the distalphalanx 120 includes a soft pad 125 including the end face 124A. In someembodiments, the pad 125 has a durometer in the range of from about 0Shore A to 60 Shore A and, in some embodiments, from about 10 Shore A to40 Shore A, and the plate member 140 has a stiffness of at least about100 GPa and, in some embodiments, at least 180 GPa.

The plate member 140 can be used to pick up, engage and/or manipulateobjects in a manner not possible or that would be cumbersome without the“fingernail”. The combination of the thin, rigid plate member 140(“fingernail”) and the pliable, soft pad 125 (“fingertip) enables thefinger to capture an edge of an object therebetween (i.e., in theundercut 146). For example, if an object is disposed on a supportsurface (e,g., a table surface), the plate member 140 can be pressedagainst the support surface, then translated under the object (betweenthe object and the support surface), and then used to lift the object.The compliant flexure joint JC compliments the functionality of thefingernail system 141. The joint compliance enables the plate member 140to adaptively align with and maintain contact with the support surface.

With reference to FIGS. 30A and 30B, the grasper 20 is shown thereinperforming a sequence of steps or movements to grasp and pick up anobject 2 (as shown, a relatively flat key) from a planar surface Z(e.g., a table or floor).

Initially, the key 2 is laid flat on the surface Z. With reference toFIG. 30A, the grasper 20 is positioned such that the extension section142 of the plate member 140 of the finger 70 is placed on the surface Zproximate the side edge 2A of the key 2 with the undercut 146 and thesoft pad 125 overlying the extension section 142. The phalanx 120 of thefinger 80 is placed against the surface Z and driven in a direction Jtoward the key 2 and the finger 70, the fingers 70 and 80 beingrelatively disposed in a pinching configuration. As the finger 80 isdriven in the direction J, it engages the side edge 2B of the key 2 andpushes the side edge 2A onto the plate member 140 (in some embodiments,into the undercut 146 and between the extension section 142 and the softpad 125). The phalanx 120 of the finger 80 is further driven toward thefinger 70 and upward to lift the side edge 2B off the surface Z. The key2 is thereby flipped or pivoted upwardly about its edge 2A and towardthe end face 124A of the finger 70 in a direction K as shown in FIG.30A, the edge 2A being captured between the plate member 140 and the pad125. With reference to FIG. 30B, the finger 80 is used to continuelifting the key 2 and converged with the finger 70 until the key 2 issandwiched between the end faces 124A of the fingers 70 and 80, whichengage the opposed faces 2D and 2C, respectively, of the key 2.

A relatively flat object such as a key (or credit card, etc.) can thusbe grasped, removed from a planar surface and manipulated using the“fingernail” or fingernails” of the grasper 20 and cooperative movementof the fingers 70, 80 (and, in some embodiments, the base 30 and/or thearm 12).

In some embodiments and as shown, the axially extending front side edges126A of the distal phalanx 120 are sharp or distinct and the front face124B (i.e., the contact or engagement face) is substantially flat orplanar (FIGS. 9 and 10). According to some embodiments, the side wallsof the distal phalanx 120 forming the side edges 126A with the frontface 124B are substantially planar at and adjacent the front face 124Band, in some embodiments, extend substantially perpendicular to theplane of the front face 124B. The front face 124B may be textured. Asshown, these edges 126A and the front face 124B can be the edges andfront face of the soft pad 125. In some embodiments, the plane of thefront face 124B is substantially parallel to the pivot pin axis FP-FPand the flexure joint primary axis FB-FB.

In use, the described configuration assists in stabilizing the distalphalanges 120. For example, when the fingers 70, 80 are used to pinch anobject between the distal phalanges 120, the sharp side edges 126A andthe planar front face 124B can reduce or eliminate the tendency of thedistal phalanges 120 to be twisted about their flexure joints JC. Thesharp edges 124A can also assist in making firm and precise engagementwith an object.

In some embodiments, the distal phalanx 120 is prismatic and has asubstantially rectangular cross-section. In some embodiments, theproximal phalanx 110 is also prismatic and has a substantiallyrectangular cross-section.

With reference to FIGS. 15-22, the grasper 20 may also be provided witha magnetic breakaway system or mechanism 150 coupling each of thefingers 70, 80, 90 to the base 30. The breakaway features for each ofthe fingers 70, 80, 90 may be substantially the same or similar andtherefore the description below with regard to the finger 70 likewiseapplies to the fingers 80 and 90.

The magnetic breakaway system 150 includes the finger base submount 40and the magnet base submount 160. A magnet 166 is fixed in the submount160 and a ferromagnetic member or plate 156 (e.g., formed of steel) isaffixed in the submount 40. A magnetic field concentrator 153 may beprovided in the submount 160.

The submount 40 has a circumferentially extending locator flange 152defining a rotational alignment slot 154 therein. The submount 160 has acircumferentially extending, semi-annular locator groove 162 having arotational alignment tab 164 therein. The locator flange 152 is seatedin the locator groove 162 such that the tab 164 is seated in the slot154. The tendon cable 60A extends through axial tendon raceways 158 and168 defined in the submounts 40 and 160, respectively. Likewise, in thecase of the finger 80, the tendon cable 62A extends through the raceways158 and 168. In the case of the thumb 90, the tendon cables 64A and 66Aextend through respective ones of the axially extending raceways 158 and168.

In use, the magnetic breakaway system 150 can serve to decouple thefingers 70, 80, 90 from the base 30 to prevent or reduce the risk ofdamage to the finger or joint. When a load on a finger exceeds aprescribed threshold load, the magnetic attraction between thecomponents 156 and 166 is overcome and the submount 40 separates(partially or fully) from the submount 160. For example, the finger 70and its submount 40 may be deflected away from the cooperating submount160 in a deflection direction G as shown in FIG. 22. When the load onthe finger is relieved (e.g., by removing an object or operating theassociated actuator to pay out the tendon cable), the magneticattraction or tension in the tendon cable will again draw the submounts40 and 160 together. For example, the finger 70 and its submount 40 mayreturn or pivot back onto the cooperating submount 160 in a returndirection H as shown in FIG. 22. The pull force of the tendon throughthe raceways 158, 168 will tend to draw the submounts 40, 160 intocoaxial alignment. In the case of a small breakaway deflection of thesubmount 40 from the submount 160, the shapes of the locator features152, 154, 162, 164 may automatically guide the submounts 40 and 160 backinto rotational alignment, whereupon the submounts 40 and 160 will againinterlock. Applying additional tension to the tendon cable may alsorotate the submounts 40 and 160 into rotational alignment. In somecases, the submounts 40 and 160 can be rotationally aligned by rotatingthe submount 160 using the actuator 68. The submount 160 will slideablyrotate relative to the corresponding submount 40 until their locatorfeatures align, whereupon the submounts 40 and 160 will nest andinterlock. In some cases, it may be necessary to manually realign andreseat the submounts 40 and 160.

In some embodiments, the magnetic breakaway system 150 does notcompromise the capability of the grasper 20 to lift heavy objects.Because the tendon cable or cables run axially through both of thesubmounts 40, 160 and substantially perpendicular to the face of themagnet 166, the tendon cables pull the submounts 40, 160 together.Typically, the submounts 40 and 160 will only be dislodged by twistingforce on the fingers.

As mentioned above and as shown in FIG. 5, the thumb 90 is provided withtwo independent tendon cables 64A and 66A connected to correspondingactuators 64 and 66. The tendon cable 64A may be regarded as an agonisttendon and the tendon cable 66A may be regarded as an antagonist tendon.

The tendon cable 64A is routed to and anchored to the distal phalanx 120of the thumb 90 in the same manner as described above. The tendon cable66A is routed through the outer raceways 158, 168, over the hingefeature 42, and anchored to the back side of the proximal phalanx 110 bya screw 43.

In addition to being operable in the same manner as described above forthe fingers 70, 80 using the tendon cable 64A, the tendon cables 64A and66A can be used together to control movement of the distal phalanx 120of the thumb 90 independently of its proximal phalanx 110. Moreparticularly, the tendon cable 66A can be used to hold the proximalphalanx 110 in place, effectively stalling the proximal phalanx 110against further rotation in the closing direction F, while the actuator64 draws on the tendon cable 64A. Because the proximal phalanx 110 isheld in place, the distal phalanx 120 is independently bent at theflexure joint JC in the direction M without simultaneous pivoting of theproximal phalanx 110 in the closing direction F. The tendon cable 66Acan be extended to permit the distal phalanx 120 to elastically bendback in the direction N about the flexure joint JC.

According to some embodiments, the tendon cables 60A, 62A, 64A, 66A arecapable of transmitting sustained tensile loads in the range of fromabout 60 to 120 lbf, exhibit low energy storage upon bending, and arerobust to bend radii less than one millimeter.

The foregoing is illustrative of the present invention and is not to beconstrued as limiting thereof. Although a few exemplary embodiments ofthis invention have been described, those skilled in the art willreadily appreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention. Therefore,it is to be understood that the foregoing is illustrative of the presentinvention and is not to be construed as limited to the specificembodiments disclosed, and that modifications to the disclosedembodiments, as well as other embodiments, are intended to be includedwithin the scope of the invention.

That which is claimed is:
 1. A compliant underactuated graspercomprising: a palm base; two fingers, wherein each of the fingerscomprises: a proximal phalanx; a distal phalanx; a compliant flexurejoint connecting the distal phalanx to the proximal phalanx; and a pinjoint connecting the proximal phalanx to the palm base, the pin jointconstraining angular movement of the proximal phalanx relative to thepalm base to rotation about a pin pivot axis; and at least one actuatorto move the fingers; wherein the grasper has fewer actuators thandegrees of freedom.
 2. The grasper of claim 1 including a pin jointangle sensor associated with each finger.
 3. The grasper of claim 1including a rotation joint connecting each finger to the palm base,wherein the finger can be rotated relative to the palm base about therotation joint to reorient its pin pivot axis with respect to the palmbase.
 4. The grasper of claim 1 further including: a thumb including: aproximal phalanx; a distal phalanx; a compliant flexure joint connectingthe distal phalanx to the proximal phalanx; and a pin joint connectingthe proximal phalanx to the palm base, the pin joint constrainingangular movement of the proximal phalanx relative to the palm base torotation about a pin pivot axis; and at least one actuator to move thethumb independently of the fingers.
 5. A compliant underactuated graspercomprising: a palm base; two fingers, wherein each of the fingerscomprises: a proximal phalanx; a distal phalanx; a compliant flexurejoint connecting the distal phalanx to the proximal phalanx; a pin jointconnecting the proximal phalanx to the palm base, the pin joint having adominant degree of freedom about a pin pivot axis; and a tendon cablefor moving the proximal and distal phalanges such that movement of thetendon cable generates angular motion of the proximal phalanx about thepin pivot axis at a greater rate than angular motion of the distalphalanx about the flexure joint; and at least one actuator to move thefingers; wherein the grasper has fewer actuators than degrees offreedom.
 6. The grasper of claim 5 wherein the flexure joint includes aflexure link formed of a compliant elastomeric material.
 7. The grasperof claim 5 wherein: the pivot joint connects the proximal phalanx to thepalm base for rotation about the pivot joint in a first direction and asecond direction; the grasper includes a return biasing spring to drivethe proximal phalanx in the second direction to a return position; thereturn biasing spring has a first spring rate; the flexure joint isconfigured to bias the distal phalanx into an open position relative tothe proximal phalanx and has a second spring rate; and the second springrate is greater than the first spring rate.
 8. The grasper of claim 7wherein the second spring rate is at least eight times the first springrate.
 9. The grasper of claim 7 wherein: the first spring rate issufficient to retain the proximal phalanx in the return position in anyorientation of the grasper with the tendon cable slack; and the secondspring rate is sufficient to retain the distal phalanx in the openposition in any orientation of the grasper with the tendon cable slack.10. A compliant underactuated grasper comprising: a palm base; twofingers, wherein each of the fingers comprises: a proximal phalanx; adistal phalanx; a compliant flexure joint connecting the distal phalanxto the proximal phalanx; a pivot joint connecting the proximal phalanxto the palm base for rotation about the pivot joint in a first directionand a second direction; a tendon cable for moving the proximal phalanxin the first direction; and a return biasing spring to drive theproximal phalanx in the second direction to a return position, whereinthe spring rate of the return biasing spring is sufficient to retain theproximal phalanx in the return position in any orientation of thegrasper with the tendon cable slack; and at least one actuatorassociated with each tendon cable; wherein the grasper has feweractuators than degrees of freedom.
 11. The grasper of claim 10 whereinthe return biasing spring includes a torsion spring.